E 
U. 8. GEOLOGICAL SURVEY BULLETIN 613 PLATE XX 
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SSCA MES TIRE Boe Bi 
A. BED OF RIO PUERCO AT NAVAJO SIDING, ARIZ. 
brim with a swiftly flowing torrent after a 
n. 
land arroyo, which Is filled to the 
rain but soon becomes dry agal 
View southwestward. A typical arid- 
B. NATURAL BRIDGE IN MASSIVE SANDSTONE NEAR THE HAYSTACK ROCKS, NORTH OF 
MANUELITO, ARIZ. 
Shows the work of a small stream which enlarged a crack along a joint plane. 
